Organometallics 1991,10, 3777-3781
3777
Migration of 1-Aikenyi Groups from Zirconium to Boron Compounds Thomas E. Cole,' Ramona Quintanilla, and Stephan Rodewald Department of Chemistty, San Diego State University, San Diego, California 92182-0328 Received August 14, 1990
Results and Discussion In this study we used the 1-hexenyl group as a representative 1-alkenyl system. The 1-hexenylzirconiumcomplex was prepared from the hydrozirconation of 1-hexyne by using freshly prepared Schwartz's reagent, Cp2ZrH(Cl).13J4 The hydrozirconationreaction is similar in many respects to the hydroboration reaction. Both reactions proceed via cis addition with a high degree of regioselectivity, placing the zirconium or boron on the terminal carbon.15 The addition of 5 mmol of the 1-hexenylzirconium complex in methylene chloride to 5 mmol of boron trichloride in hexane at 0 "C rapidly formed an off-white precipitate. Analysis of the reaction mixture by The hydrozirconation of alkynes has been shown to be "B NMR revealed a new signal at +52.7 ppm, which is useful for the preparation of alkenylzirconium compounds.' consistent with the migration of the vinyl group. Since Unfortunately, these dicyclopentadienylzirconium alkenyl trivinylborane and all vinylchloroboranes have similar chlorides do not generally undergo carbon-carbon bondchemical shifts, ca. +55 ppm, the reaction mixture was forming reactions. To overcome this limitation, transmethanolyzed with an excess of methanol, forming the metalation to other metals whose ability to form carboncarbon bonds such as aluminum:+ copper,S p a l l a d i ~ m , ~ readily distinguishable derivatives. In this reaction a new major peak was observed at +27.4 ppm, which corremercury! tin,' and zinc7 has been explored. In principle, sponded to the vinyl boronic ester, and only small amounts transmetalation should proceed to a more electronegative of materials were seen a t +18.4 ppm (B(OMe)3from unmetal than zirconium. As such, one would expect that reacted BC13) and at +47.6 ppm (divinyl borinic ester). organic groups would migrate from zirconium to boron. The llB NMR spectra indicated an approximately 90% Organoboranes are one of the most versatile intermeconversion to 1-hexenyldichloroborane. This suggested diates and one of the most intensely studied of the orselective migr,ation of the 1-hexenyl group to form the ganometalli~s.**~The variety of products that can be monovinylborane. The 1-hexenyldimethoxyborane was prepared via organoboranes is essentially only limited by isolated and analyzed by both lH and 13CNMR. Analysis the types of organic groups that can be placed on boron. of the chemical shifts and coupling constants confirmed There are obvious advantages in combining the unique a pure trans stereochemical assignment of the 1-hexenyl reactivity and selectivity of organotransition metals with group within the limib of detection by NMR (90
52.1
27.4
53
28.5
30.9
27.2
>90
26.9
30.5
27.2
23.5
25.8
-70
22.8
26.0
-
chem shift
product
BCl:,
41.9
CI,BJBu
BBra
38.5
B r , B J B U
40
-1.7'
83.6
%
>90
B B - B r
B(OMeh
B
8-OMe
76.2
73.4
79.0
76.5
76.5
>90
73.8
73.8
-50
18.2 56.4
(MWZB*Bu
27.0 76.4
JLBY
-90
-
15
25
OPyridine added in place of methanol to form the pyridine complex. 9-BBNn thexylhexylchloroborane;28B-chlorodiisopropoxyborane; B-chloro-1,3,2-dioxaborinane;=B-chlorodicyclohexylborane.~~31 Solvents used were ACS grade and were dried prior to use. Manipulation of borane reagents was done under nitgrogen atmosphere by using hypodermic and double-ended needles and solids were handled in a glovebag.32 The 'H, "B, and 13CNMR spectra were recorded with a Chemagnetics 200-MHz spectrometer. Chemical shift values are given in parts per million (6) relative to Me& for 'H and 13C NMR and relative to BF,.OEt, in 'lB NMR. GC-MS was performed on a Finnigan 3000 GC/MS + 6110 MS data system. Preparation of Dicyclopentadienyl-1-hexenylzirconium Chloride.' To a 50-mL flask was a septum-covered side arm, equipped with a magnetic stirring bar and adapter, was added 20 mmol of Schwartz's reagent, Cp2ZrH(C1)(5.16 g), suspended in 15 mL of methylene chloride. The mixture was cooled to 0 "C and 22 mmol 1-hexyne (1.81 g, 2.50 mL) was slowly added, followed by an additional 2.50 mL of methylene chloride to give an approximate 1M solution. After 15-30 min, the solid disappeared to give a clear yellow solution: 'H NMR (CDCl,) 6 6.80 (27) Brown, H. C.; Cha, J. S.; Nazer, B.; Brown, C. A. J. Org. Chem. 1986,50,549. (28) Brown, H. C.; Sikorski, J. A. J. Org. Chem. 1982,47,872. (29) Finch, A.; Lockhart, J. C.; P e w , J. J. Org. Chem. 1961,213,3260. (30) Brown, H.C.; Ravindran, H. J . Org. Chem. 1977,42, 2533. (31) Zweifel, G.;Peareon, N. R. J. Am. Chem. SOC.1980, 102,5919. (32) Brown, H. C.; Kramer, G.W.; Levy, A. B.; Midland, M. M. Organic Syntheses uia Boranes; Wiley-Interscience: New York, 1975; Chapter 9.
(dt, 1H, J = 18 Hz), 6.22 (8, 10 H), 5.76 (d, 1H, J = 18 Hz), 1.93 (9,2 H), 1.32 (m,4 HI, 0.89 (t, 3 H). General Procedure for the Transmetalation from Zirconium to Boron. To a 25-mL flask with a septum-covered side arm, equipped with a magnetic stirring bar and adapter, was added ca. 5 mmol of the borane in 5 mL of methylene chloride. The solution was cooled to 0 "C and a stoichiometric amount of the dicyclopentadienyl-1-hexenylzirconiumchloride solution was added. The reaction forms an off-white precipitate, generally within 15-30 min. The extent of reaction can be estimated by using the ratio of peak areas in the llB NMR. This method appears to give satisfactory results for boron-containing species with similar peak widths. The comparison of this method with weighted mixtures of the pure authentic boron products agreed within f 3 % . This procedure has also been used to estimate the concentration of organolithiums by reacting with trialkoxyboranea and analyzing by llB NMFLS Nbth and Wrackmeyer have also reported using this method to determine ratios of boron products in equilibrium mixturesqU To distinguish between borane products that have similar chemical shifts, the reactions mixtuns were analyzed both before and after methanolysia or complexation with a suitable base such as pyridine. Table I summarizes the results of these reactions. Products were isolated by first separating the solids from the reaction mixture and the solvent was removed under reduced pressure. The residue was extracted with (33) Brown, H. C.; Cole, T. E. Organometallics 198S, 2, 1316. (34) Biffar, W.; Nivth, H.; Pommerening, H.; Wrsckmeyer, B. Chem. Eer. 1980, 113, 333.
3780 Organometallics, Vol. 10, No. 10, 1991 4 x 5 mL of pentane followed by removal of the pentane from the combined extra& to yield pure product, as indicated by NMR. Preparation of (E)-l-Hexenyldichloroborane?6 The preparation was conducted as in the general procedure by adding 5 mmol of the dicyclopentadienyl-1-hexenylzirconiumchloride solution to boron trichloride in methylene chloride (5 mmol, 5 mL): llB NMR (CHZCI2)+53.0 ppm, after methanolysis +27.4 ppm, >90% product ratio based on "B NMR. In order to assign the stereochemistry of the vinyl group, the (E)-1-hexenyldichloroboranewas isolated from the reaction mixture and converted into the corresponding methyl ester and analyzed by NMR spectroscopyfor retention of the trans stereochemistry as reported by Brown.% Spectroscopic data are in agreement with reported values, indicating retention of the 1-alkenyl group. 'H NMR (CDC13) 6 6.52 (dt, 1H, J = 18 Hz), 5.42 (d, 1H, J = 18 Hz), 2.13 (m, 2 H), 1.30 (m, 4 H), 0.90 (t, 3 H); 13CNMR (CDC13)6 152.00, 50.89, 35.30, 30.57, 22.30, 13.97. Preparation of ( E ) -l-Hexenyldibromoborane.37 As in the general procedure, 5 mmol of the dicyclopentadienyl-l-hexenylzirconium chloride solution was added to boron tribromide in methylene chloride (5 mmol,5 mL): I'B NMR (CHzCId 6 +52.1 ppm, after methanolysis +27.4 ppm, 53% ratio of boron containing materials. Preparation of B-(E)-l-He~enyl-l,3f-dioxaborazole.~ The preparation was conducted as in the general procedure by adding 9.9 mmol of the dicyclopentadienyl-1-hexenylzirconiumchloride solution to 9.9 mmol of B-chlorocatecholborane (1.529 g) in 10 mL of methylene chloride. The same experiment was also conducted by using 10 mmol of B-bromocatecholborane (0.994 g) in methylene chloride and the product characterized by "B: "B NMR (CH2CI,) 6 +30.5 (Br), +30.9 ppm (Cl), after methanolysis +27.2 ppm, >90% product ratio for both reactions. The Bchlorocatecholborane derivative was isolated as in the general procedure to yield 1.133 g or 57% B-(E)-l-hexenyl-1,3,2-dioxaborazole. Spectroscopicdata are in agreement with expected and reported llB NMR (CDC13)d 31.1; 'H NMR (CDC13) 6 7.24-7.06 (m, 5 H), 5.73 (d, 1 H, J = 18.0 Hz), 2.19 (q, 2 H, J = 6.4 Hz),1.5-1.2 (m, 4 H), 0.88 (t, 3 H, J = 7.3 Hz); 13C NMR (CDClJ 6 15758,148.36,122.24,115.58, 112.09,35.63,30.25,22.19, 13.70; IR (neat) 3063, 2959, 2929, 2860, 1640, 1474, 1402, 1375, 1334, 997, 810, 741 cm-'. E1 mass spectrum: m/z (relative intensity) 202 (M', 46), 173 (20), 160 (71), 159 (34), 146 (loo), 145 (39), 120 (40), 67 (31), 65 (39). Preparation of ( E ) - l - H e ~ e n y l - 9 - B B N from ~ ~ B-Bromo9-BBN. Ten millimoles of the dicyclopentadienyl-l-hexenylzirconium chloride solution was added to B-bromo-9-BBN in methylene chloride (10 mmol, 10 mL). To distinguish between starting material and the vinyl-9-BBN product, 5 mmol of pyridine was added, forming the borane amine complexes: "B NMR (CH2C12)6 -1.70 ppm, >90% ratio of boron-containing materials. Isolation of the compound afforded 1.71 g or 84% yield of (E)-l-hexenyl-g-BBN. Spectroscopic data are in agreement with expected and reported values.39 "B NMR (CDCI3)6 77.4; 'H NMR (CDCl3) 6 6.84 (dt, 1 H, J = 6.4, 17.5 Hz), 6.22 (d, 1 H, J = 17.3 Hz),2.26 (q,2 H, J = 6.9 Hz), 2.00-1.65 (m, 12 H), 1.60-1.15 (m, 6 HI, 0.95 (t, 3 H, J = 7.6 Hz); 13C NMR (CH2Clz)6 156.38, 36.12,34.08,31.02, 28.87,22.69,14.04; IR (neat) 2927,1635, 1613, 1468,1447,1381,1333,999cm-'. E1 mass spectrum, m/z (relative intensity) 206 (M+,27), 148 (22), 147 (20), 134 (43), 133 (37), 120 (721, 119 (52), 108 (26), 106 (41), 105 (40), 93 (54), 92 (89). Preparation of 1-Hexenyldicyclohe~ylborane?3The dicyclohexylchloroborane was prepared by the procedure reported by Brownmor from the addition of anhydrous hydrogen chloride to dicylohexylborane using the procedure of Z ~ e i f e l . ~By ' use of the general procedure, 10 mmol of the dicyclopentadienyl-lhexenylzirconium chloride solution was added to the dialkylcholorborane. The product was isolated in a 64% isolated yield (36)Brown, H.C.; Ravindran, N. J.Am. Chem. SOC.1976,98, 1798. (36) Brown, H. C.; Bhat, N. G.; Somayaji, V. Organometallics 1989, 2, 1311. (37) Brown, H.C.; Campbell, J. B.J. Org. Chem. 1980,45, 389. (38) Yatagai, H.; Yamamoto, Y.; Maruyama, K. J. Org. Chem. 1979, 44. 2588. (39) Soderquist,J. A,; Colberg, J. C.; Del Valle, L. J.Am. Chem. SOC. 1989, 11 1,4873.
Notes (1.66 9). Spectroscopic data are in agreement with expected and previously reported values." llB NMR (CDC13) 8 73; 'H NMR (CDClj) 6 6.72 (dt, 1 H, J = 17.6,6.3 Hz), 6.20 (d, 1 H, J = 17.5 Hz), 2.21 (4,2 H, J = 6.7 Hz),1.72 (m, 10 H), 1.46-1.26 (m, 16 H), 0.91 (t, 3 H, J = 6.8 Hz); "C NMR (CDCl3) 6 154.11, 133.65, 36.11, 34.44,30.90,27.83,27.67, 27.24, 22.41,13.92; IR (neat) 3078, 2958, 2921, 2847, 1612, 1447, 1371, 1145,997 cm-'. Preparation of B-(E)-l-Hexenyl-1,3,2-dioxaborinane,'B The dioxaborinane (10 mmol) was prepared by the procedure reported by Finch, redistributing boron trichloride in methylene chloride (3.35 mmol, 3.35 mL) with 6.6 mmol of trimethylene borate (1.624 g, 1.4 mL).29 Using the general procedure, 10 mmol of the dicyclopentadienyl-1-hexenylzirconium chloride solution was added to the freshly prepared B-chloro-l,3,2-dioxaborinane: llB NMR (CH,Cl,) +25.8 ppm, in an approximate 70% product ratio. The product was obtained in a 41% isolated yield (0.652 9). Spectroscopic data are in agreement with expected and reported values.16 llB NMR (CDC13)d 26.97; 'H NMR (CDCIJ d 6.47 (dt, 1 H, J = 6.3, 17.8 Hz), 5.32 (d, 1 H, J = 17.8 Hz),3.98 (t, 4 H, J = 5.6 Hz), 2.10 (9, 2 H, J = 7.1 Hz), 1.92 (p, 2 H), 1.55-1.20 (m, 4 H), 0.88 (t,3 H, J = 7.3 Hz); 13CNMR (CDC13) 6 150.78, 123.32,61.20, 34.82, 30.41, 27.24, 21.87, 13.43; IR (neat) 2957,2873,1640,1484,1421,1326,1000,911,735 cm-'; E1 mass spectrum, m/z (relative intensity) 168 (M+, lo), 153 (lo), 140 (34), 139 (44), 126 (loo), 125 (58), 111 (58), 97 (51), 86 (86). Preparation of l-Bromo-l-hexyne.u To a 250-mL ilask with a septum-covered side arm, equipped with a magnetic stirring bar and adapted, was added 18 g (300 mmol) of potassium hydroxide and 100 mL of water was added to dissolve the alkali. The mixture was cooled to 0 "C and 50 mmol of bromine (2.75 mL) was added dropwise over 15 min. Fifty millimoles of 1-hexyne (4.1 g, 5.75 mL) was added to this mixture at 0 OC and the solution was allowed to stir and come to room temperature overnight. The aqueous layer was extracted with ether (3 X 25 mL). The ether extracts were dried over anhydrous magnesium sulfate; then, after removal of the solvent, the product was isolated by distillation. Isolated yield: 4.51 g (56%) of 1-bromo-1-hexyne, bp 44-47 OC (18mmHg): 'H NMR (CDCI3)6 2.20 (t,2 H), 1.46 (m, 4 H), 0.91 (t,3 H), E1 mass spectrum, m/z (relative intensity) 160 (M+,1001, 162 (M + 2+, 99), 147 (30), 145 (34), 119 (loo), 117 (loo),115 (SO), 81 (loo), 79 (100). Preparation of 5,7-Tetradecadiene.% 1-Bromel-hexyne was hydroborated at 0 "C with 1.0 M dibromoborane-methyl sulfide in methylene chloride (24 mmol, 24 mL). Dicyclopentadienylwas prepared in the same 1-octenylzirconiumchloride (25 "01) manner as previously reported for hydrozirconationreactions. The zirconocene complex was added a t 0 "C to the dibromoalkenylborane and after 15 min an off-white precipitate appeared. After removal of the precipitate, the dialkenylbromoboranewas isolated by evaporation of the solvent under reduced pressure. The borane was then dissolved in 50 mL of THF and 3.89 g (72 mmol) of sodium methoxide in 72 mL of methanol was added at -25 OC. The cold bath was removed after 5 min and stirring was continued for 1 h at room temperature. The solvents were removed under reduced pressure. The flask was fitted with a reflux condenser and the vinylborane was protonated by using 25 mL of isobutyric acid under reflux conditions for 3 h. The reaction was cooled and added to 100 mL of water and extracted with diethyl ether (6 X 25 mL). The ether extract was washed with a saturated aqueous solution of sodium carbonate to remove isobutyric acid and then oxidized with 8.5 mL of 3 M NaOH and 8.5 mL of 30% HzOZto remove boron-containing materials. The aqueous layer was extracted again with diethyl ether and the combined ether layers were dried over magnesium sulfate. The solvent was removed at reduced pressure and the product was distilled to give 2.27 g (49%) of the trans,trans-5,7-tetradecadiene,bp 65-70 O C (0.5 mmHg). Spectroscopicdata are in agreement with expected and reported values:26 'H NMR (CDClJ d 6.0 (d, 2 H, J = 14.6 Hz), 5.56 (dt, 2 H, J = 14.6 Hz), 2.05 (q,4 H), 1.30 (m, 12 H),0.89 (t, 6 H); IR (neat) 3015,2959,2928,2857,1626,1467,990,906 cm"; E1 ma88 spectrum, m / z (relative intensity) 194 (M+, 161,123 (15), 110 (46), 109 (29), 96 (38), 95 (62), 82 (71), 81 (100).
Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research.
Organometallics 1991,10,3781-3785 Registry No. Cp.&H(Cl), 37342-97-5; BC13, 10294-34-5;BBr,, 10294-33-4;B(OMe)B,121-43-7; E-bromo-g-BBN, 22086-45-9; E-methoxy-g-BBN,38050-71-4; E-(E)-l-hexenyl-9-BBNpyridine complex, 136115-27-0;E-(E)-l-hexenyl-g-BBN,69322-45-8; 1hexyne, 693-02-7; bis(cyclopentadieny1)-1-hexenylzirconium chloride, 79083-22-0; bis(cyclopentadieny1)-1-octenylzirconium chloride, 63175-90-6; E-chlorocatecholborane, 55718-76-8; Bbromocatecholborane, 51901-85-0;B-chloro-1,3,2-dioxaborinane, 1003-43-6; E-chlorodiisopropoxyborane, 66009-09-4; dicyclohexylchloroborane, 36140-19-9; E-chlorohexylhexylborane, 88817-20-3; E-chlorodiisopinocamphenylborane,85116-37-6;
3781
(E)-1-hexenyldichloroborane,51207-21-7; (E)-1-hexenyldibromoborane,72228558; E-(E)-l-hexenyl-1,3,2-be~oxaborole, 37490-22-5; B-(E)-l-hexenyl-1,3,2-dioxaborinane, 91083-28-2; (E)-1-hexenyldiisopropoxyborane,91083-27-1; (E)-1-hexenyldicyclohexylborane,37609-12-4;thexylhexyl-(E)-1-hexenylborane, 136089-08-2; B- (E)- 1-hexenyldiisopinocamphenylborane,7017928-1; (E)-1-hexenyldimethoxyborane, 91083-26-0; l-bromo-lhexyne, 1119-64-8; dibromoborane-methyl sulfide, 55671-55-1; (1-bromo-1-hexenyl)dibromoborane,136089-09-3; (l-bromo-lhexeny1)-1-octenylbromoborane,136089-10-6; isobutyric acid, 79-31-2; trans,trans-5,7-tetradecadiene, 73349-16-3.
Synthesis of Cadmium Pentamethylcyclopentadlenyl Complexes C. C. Cummins, R. R. Schrock,' and W. M. Davis Department of Chemistry, Massachusetts Institute of Technoiogy, Cambridge, Massachusetts 02 139 Received April 22, 799 7
Summary: The preparation of red, light-sensitive cadmium bis(pentamethylcyc1opentadienide) has been effected by reaction of Cd(acac), with 2 equiv of LiCp' in the dark. CdCp', forms a weak adduct with 1,Pdimethoxyethane (DME). A Schlenk-type equilibrium exists when CdCp', is mixed with an equimolar amount of Cd[N(SiMe3),],, giving solutions from which (CdCp' [N(SiMe3),]), can be crystallized. Single-crystal X-ray diffraction revealed the dimeric nature of the latter complex, which displays bridging silylamides and terminal Cp' ligands. Bonding of the Cp' ligand to cadmium in this complex is regarded primarily as u in character, but a weak dative interaction between the diene HOMO and the empty cadmium pz orbital is plausible in view of structural parameters. The structure determination is believed to be the first on any complex containing either a cadmium amide or a cadmium pentamethylcyclopentadienide linkage.
Introduction Cadmium compounds that contain bulky ligands are currently of interest with respect to the design of molecular precursors to semiconductors such as CdS and CdSe.' thiophenoxide,lb and selenophenoxidelb complexes are examples that recently have been synthesized with this purpose in mind. The absence of pentamethylcyclopentadienyl (Cp*) complexes in the list is especially surprising, since the Cp* ligand has been useful in stabilizing a wide variety of low-coordinate compounds that contain metals throughout the periodic tablea2 We became interested in preparing Cp* cadmium complexes as part of a project concerned with the synthesis of semiconductor clusters employing ROMP block copolymer te~hnology.~ (1) (a) Bauch, C. G.;Johnson, C. E. Inorg. Chim. Acta 1989,164,165. (b) Bochmann, M.; Webb, K.; Herman, M.; Hursthouse, M. B. Angew. Chem., Int. Ed. Engl. 1990,29, 638. (2) Collman, J. P.; Hegedua, L. S.; Norton, J. R.; Finke, R. G.&incipler and Applicatiom of Orgonotramition Metal Chemistry; University Science Books: Mill Valley, CA , 1987. (3) (a) Sankaran, V.; Cummins, C. C.; Schrock, R. R.; Cohen, R. E.; Silbey, R. J. J . Am. Chem. SOC.1990, 112, 6858. (b) Cummins, C. C.; Beachy, M. D.; Schrock, R. R.; Vale, M. G.;Sankaran, V.; Cohen, R. E. Submitted for publication.
Scheme I Mx + Licp*
-
Lv
Mx"
MCp* path B
- Mo
\
1
+
1: Cp.'
*;
+
Li+ path A
It is reported in the literature that CdC12is efficiently reduced by LiCp* in tetrahydrofuran (THF)to give colloidal cadmium, LiC1, and CIoMelO(eq l).4 Although
aa* +
2LiCp.
-
+
a 0
+ 2LiQ
(1)
details of this reaction are not known, CloMe10most likely is formed via coupling of C5Me5radicals, which are known to be generated upon oxidation of C5Me5-or upon photolysis of Cp* derivatives (including the parent hydrocarbon, C5Me5H)and to combine to give CloMe10at diffusion-controlled rates.5 Interestingly, Jutzi and Kohl expressed doubt that the original report6 of HgCp*2 is correct, since its reported 'H NMR spectrum is virtually identical with that obtained by them for CloMelo,which they produced by adding pyridine to SnCp*J2.' It also (4) Blom, R. Acta Chem. Scand. 1988, A42, 445. This reference describes the gas-phase structure of Cl&elo; for the crystalline structure of the hydrocarbon see: Lorberth. J.: et al. Abstracts of the XIIIth ICOC; Turin, italy, 1988. (5) Davies, A. G.; Lusztyk, J. J . Chem. Soc., Perkin T M ~2 1981,692. . (6) Floris. B.: Illuminati.. G.:. Ortanni. G. J . Chem. Soc.. Chem. Commuh: 1969, 492.' (7) Jutzi, P.; Kohl, F. J . Organomet. Chem. 1979,164, 141. I I
0276-7333/91/2310-3781$02.50/00 1991 American Chemical Society
